The ongoing investigations in my laboratory are focused on delineating immunomodulatory mechanisms of innate and adaptive immune responses. I have developed a novel ex vivo system for proliferating and differentiating large numbers of functional dendritic cells, from Sca-1+Lin- hematopoietic progenitor cells (HPC). Using a combination of myeloid and stromal growth factors the murine bone marrow derived HPC used in these experiments average 613 plus/minus 65 fold expansion. The resulting cells are a fairly homogeneous population of cells that express moderate to high levels of surface and intracellular molecules that are characteristic of immature myeloid dendritic cells. In the presence of additional immunomodulatory cytokines the myeloid dendritic cell precursors mature into efficient lymphocyte stimulators. In parallel experiments I have successfully transduced the HPC with a retroviral vector, and successfully culture the cells as indicated above into myeloid dendritic cell precursors. Using this ex vivo system we have identified an immediate precursor of immature murine myeloid dendritic cells. In addition this ex vivo culture system delineates a sequential pathway from a defined murine hematopoietic progenitor cell to a dendritic cell precursor, to an immature dendritic cell, to a functionally mature dendritic cell. Our system shows that the culture environment, combination and concentration of cytokines, as well as the time of delivery of cytokines to the culture are definitive to the ultimate cell differentiation and function. Although all aerobic cells are capable of producing reactive oxygen species (ROS) such as superoxide and hydrogen peroxide, ROS mediated tissue injury is routine at sites of acute infection and inflammation. The phagocyte NADPH oxidase has been recognized as the primary antimicrobial host defense system used to protect against pathogenic microorganisms. The NADPH oxidase is a multi-component enzyme complex. The membrane-associated flavo-cytochromeb558 is composed of the gp91phox and p22phox subunits. p47phox, p67phox and the regulatory GTPase Rac2 are the three cytosolic factors which complex with the membrane cytochromeb558 upon cell activation. In activated phagocytes from normal host cells this complex mediates the transfer of an electron to molecular oxygen and leads to the production of a superoxide anion along with other products of oxidative metabolism including hydrogen peroxide, hydroxyl radicals and hypochlorous acid. The enzyme complex is present in all professional phagocytes (macrophages, neutrophils, eosinophils) and also in B lymphocytes. We have developed and characterized a murine model for the most common autosomal recessive form of phagocyte NADPH oxidase deficiency, the 47phox deficient model of Chronic Granulomatous disease (CGD). Recent investigations in my laboratory lead to the observation that T cell receptor stimulated T lymphocytes generate three discrete ROS events. The T cell receptor stimulated prolonged phase of hydrogen peroxide release is phagocyte NADPH oxidase dependent. In addition T cell receptor stimulation skews cytokine secretion towards a T helper 1 phenotype in NADPH oxidase deficient T cell blasts. Our results indicate that mature T cells express a phagocyte-type NADPH oxidase that regulates various elements of T cell receptor signaling. Recent investigations have also revealed that dendritic cells express functional phagocyte - type NADPH oxidase activity. The aim of this project is to characterize the involvement of the NADPH oxidase in the regulation of dendritic cell and T cell biology.